PAC vs STAC Code: What's the Difference and Which Do You Need?

Last Updated: July 2026

Switching mobile networks in the UK is now easier than ever thanks to Ofcom's "Text-to-Switch" rules. Whether you want to keep your existing phone number or start completely fresh with a new one, you will need either a PAC or a STAC code. In this comprehensive guide, we explain the technical difference, the exact timelines, and how to avoid common billing traps when leaving your current provider.

What is a PAC Code? (Keep Your Number)

A PAC stands for Porting Authorisation Code. It is a unique 9-character alphanumeric code (e.g., ABC123456) that gives your new mobile provider the legal authority to take over your existing phone number.

You should request a PAC code if you are leaving your current network (like EE, O2, Vodafone, or Three) but you absolutely want to keep your current phone number. This is crucial for businesses, freelancers, and anyone who doesn't want the hassle of updating their contacts, bank details, and WhatsApp accounts with a new number.

What is a STAC Code? (Get a New Number)

A STAC stands for Service Termination Authorisation Code. Like a PAC, it is a 9-character code, but its function is entirely different.

You should request a STAC code if you want to cancel your current mobile contract and move to a new provider, but you do not want to keep your old number. Providing a STAC to your new network tells them: "Please terminate my old contract at my old network, but give me a brand new number on your network."

The Automated Cancellation Benefit

The greatest advantage of both PAC and STAC codes is that they trigger an automatic cancellation of your old contract. You never have to call your old provider, sit on hold, or deal with high-pressure retention sales tactics. Once your new network processes the code, your old billing account is automatically closed.

However, if you are still within your minimum contract period (e.g., month 12 of a 24-month contract), you will still be billed an Early Termination Fee (ETF) on your final invoice.

Porting Timelines & "Double Billing"

A PAC or STAC code is valid for exactly 30 days from the moment you request it. If you do not give it to a new provider within that timeframe, the code simply expires, and your current contract continues as normal.

When you hand your PAC code to your new provider (like SecondSim), the porting process typically takes one working day. During this day, your old SIM will continue to work. You will only experience a brief loss of service (usually 10-15 minutes) on the day of the transfer when the number physically moves across networks.

Avoid Notice Periods: Under Ofcom rules, using a PAC or STAC code means you do not have to give a 30-day notice period to your old network. This prevents "double billing" where you end up paying two networks for the same month of service.

Switching to a Business eSIM

If you are switching from a physical SIM to an eSIM, the PAC process remains exactly the same. You activate the eSIM on your new device, log into your new provider's dashboard, and input the PAC code. The network routes your old number onto the digital eSIM profile.